Final answer:
Two typical test-cross ratios in genetics are 0.25 and 0.50. A classic Mendelian dihybrid cross ratio is 9:3:3:1, and a 1:1 ratio in a test cross suggests a heterozygous parent for the examined trait.
Step-by-step explanation:
Two typical test-cross ratios are 0.25 and 0.50. A dihybrid cross ratio that totals 16 is typical of a two-gene interaction, with the classic Mendelian example being 9:3:3:1.
This ratio is derived from considering two non-interacting genes. When gene pairs interact, we would also expect ratios expressed as 16 parts, such as 9:3:3:1, as long as we assume that the interacting genes are independently assorting into gametes.
In the context of a test cross, a 1:1 phenotypic ratio suggests that one parent is heterozygous for the trait in question. For example, if a test cross results in a 1:1 ratio of yellow to green offspring, this indicates that the parental organism is heterozygous for the gene responsible for the color trait.
When conducting a test cross in genetics, there are two typical ratios that can be observed. The first ratio is a 1:1 ratio between the dominant and recessive phenotypes.
This indicates that the parent is heterozygous for the gene in question. The second ratio is a 1:2:1 ratio, where the dominant phenotype appears twice as often as the recessive phenotype. This indicates that both parents are heterozygous for the gene.